Additional contributor: Agustin Dalmasso (faculty mentor).Interspecies organ transplantation offers a potential strategy to the global shortage in vital
human organs for donation. Multiple obstacles remain before rejection of foreign organ
grafts (xenotransplantation) can be avoided. In pig-to-primate combinations, the vascular
endothelium of the transplant is the main target of injury by the host immune system. We are
using an in vitro system in which pig endothelial cells (EC) are modified to make them
resistant to injury by anti-EC antibodies (abs) in human blood. These abs damage the EC by
causing cellular retraction and intercellular gap formation. My aim is to study methods and
mechanisms that protect the EC from injury caused by the abs. The cytokine interleukin-4
(IL-4) induces protection of EC from apoptosis and from killing by human complement. My
results demonstrated that pretreatment of the EC with pig IL-4 decreases the amount of abinduced
cellular retraction and intercellular gap formation. This finding suggested that IL-4
might regulate the expression of proteins that maintain cell-to-cell junctions in the monolayer.
Using immunofluoresce, we examined the expression of the junction proteins CD31, VEcadherin,
and claudin-5, in IL-4-treated and untreated EC. We found that IL-4 strongly
induces claudin-5 expression, but not expression of VE-cadherin or CD31. We now plan to
use siRNA silencing of claudin-5 to investigate whether increases in claudin-5 protein are
important for protection of EC from ab-induced damage. If this silencing abolishes EC
protection, claudin-5 must play a pivotal role in IL-4-induced protection. Conversely, if
protection still occurs, claudin-5 is an unnecessary side reaction of the protection. This
information will help uncover mechanisms behind IL-4 induced protection, and contribute to
new approaches for xenotransplantation
